Flame retarding linear polyesters and shaped articles thereof

ABSTRACT

Flame-repellant linear polyesters are obtained by incorporating by condensation phosphorus-compounds having the formula ##STR1## wherein R and R 1  are organic radicals which may also contain hereto atoms into the linear polyesters, preferably those from terephthalic acid and ethylene glycol. These polyesters are materials of which flame-repellent filaments, fibers, sheets, press-moulded and injection-moulded articles may be made. Products of the invention can be used whereever especially acute risks of ignition and fire exist.

.Iadd.This is a continuation of application Ser. No. 880,866 filed Feb.23, 1978, now abandoned. .Iaddend.

It is an object of the present invention to provide flame retardedsynthetic linear polyesters modified with carboxy-phosphinic acids, aswell as articles shaped from these modified polyesters.

It is known that shaped articles, such as filaments and fibers can beprepared from linear polyesters which comprise in the polymer moleculephosphorus-containing compounds. In these cases, various acids ofphosphorus and their derivatives were especially used asphosphorus-containing modification-compounds, e.g. also phosphonic acidsand phosphinic acids. Thus, the German Auslegeschrift No. 1,243,819describes filaments and fibers made from polyesters modified withphosphonic acid esters. The filaments and fibers are well suited fordyeing with basic and disperse dyestuffs and have a low pillingtendency.

Phosphonic and phosphinic acids or their esters are added in course ofthe processes for the preparation of fiber-forming linear polyesters,according to the disclosures in German Offenlegungsschrift No. 1,520,079and German Offenlegungsschrift No. 1,595,598, and incorporated into thepolymer chains. The main purpose of this modification is also to improvethe dyeing properties of the corresponding filaments and fibers, andimprovement in dyeing properties is the sole purpose of the polyestermodification with bis-(p-carboxyphenyl)-phosphinic acid described byGerman Auslegeschrift No. 1,232,348.

However, it is also known that polyesters comprisingphosphorus-containing compounds may have flame-repellent properties.Thus, French Pat. No. 1,196,971 discloses copolyesters having phosphonicacid units, and being resistant to flames and heat. These copolyesterproducts can be used as flame-protection agents, adhesives, varnish andimpregnating substances for paper and textiles as well as intermediateproducts. On the other hand, it is not possible to spin these polyestersto yield filaments or fibers, since their phosphorus content impartsbrittleness to the products.

Furthermore, it has been suggested that flame-repellent polyesters beprepared by incorporating by condensation into the polyester moleculesalkylene-diphosphinic acids, arylene-di-phosphinic acids oraralkylene-di-phosphinic acids which may also contain additional heteroatoms such as F, Cl, Br, O and S. These polyesters can be worked up tofilaments, fibers and to shaped articles (German OffenlegungsschriftNos. 2,236,037, 2,328,343, 2,236,038 and 2,236,039). But, due to theiroccasionally rather considerable volatility at the condensationtemperatures, it is quite difficult to incorporate the diphosphinicacids by condensation. Therefore, non-volatile oligomers of diphosphinicacids with diols are often used and incorporated in the polyester bycondensation. In such cases it is, of course, necessary to first preparethe oligomers.

Another method for preparation of flame-repellent polyesters has alsobeen plasticized which involves incorporating phosphorus compounds intothe polyester in such a way that they are not built into the polymerchains. According to the two Japanese Pat. Nos. 7,142,230 and 7,142,231certain esters of phosphoric acid and halogen-containing aromaticdihydroxy-compounds have been used as such additives and according toBelgian Pat. No. 769,229 special polyphosphonates andpoly(phosphonate-phosphates) have been similarly used. While the use ofthese additives provides good flame-protection properties, theflame-protection is not permanent and the products are subject tocertain other disadvantages. These advantages are especially aconsequence of the considerable tendency of the additives to migrate asa result of which the polymer products have a certain toxicity and theadditives can be washed out relatively easily, e.g. in the course of drycleaning of articles made of corresponding fibers. When the additivesare washed out of the articles, the polymer products, of course, losetheir flame-repellent properties.

In the course of the preparation of such fibers, the additives are oftenresponsible for sticking together of the polymer chips during the dryingprocess, as a consequence of the additives tending to migrate to thesurface of the polymer chips. The quite highly-viscous polymer additivesdescribed in Belgian Pat. No. 769,229 have a viscosity such that mixingthem homogeneously with the polyesters is rather difficult. Moreover,they cause undesirably high diglycol contents in cases where theadditives are blended in while the polyester-forming reaction is stillgoing on.

A comparison of these polymers with polymers in which, phosphoruscompounds are incorporated into the chain molecules shows the polymerswith the additives in question have poorer dyeing properties. Even redphosphorus has been used as an additive for producing flame-repellentand self-extinguishing properties of polyester fibers and filaments(German Offenlegungsschrift No. 2,148,348).

Even though such filaments and fibers are sufficiently flame-repellentor self-extinguishing, the addition of red phosphorus does not permitwhite products to be obtained. Thus the products obtained are of limiteduse only.

Therefore, it is an object of the present invention to producepermanently flame-retarding linear polyesters by using an appropriatemodify agent which imparts flame-repellent properties to filaments andfibers spun therefrom the textile properties of which compare favorablywith those of filaments and fibers made of the correspondingnon-modified polyesters, and which also permit a work-up to yield usefulsheets and shaped articles. Moreover, the modification agent should notbe volatile during the process of incorporation by condensation.

The problems outlined above have been solved by the modified linearpolyesters of the present invention. These modified polyesters consistof dicarboxylic acid components and diol-components as well as ofphosphorus-containing chain members and comprise phosphorus-containingchain members having structural units of the formula ##STR2## whichconstitute about 3 to 20 mol. % of the acid component of the polyester.

In this formula R is a saturated open-chained or cyclic alkylene-radicalhaving from one to 15, preferably from two to 10 carbon atoms or anarylene or aralkylene-radical for example ##STR3## and R₁ is an alkylradical having up to six carbon atoms, an aryl radical or an aralkylradical for example CH₃, C₂ H₅, n- and i-C₄ H₉, C₅ H₁₁, C₆ H₁₃, C₆ H₅,C₆ H₅ -CH₂ etc.).

Preferred phosphorus-containing chain members are the structural unitsof the above formula with R being --CH₂ --CH₂ -- or C₆ H₄ and R₁ beingCH₃ or C₆ H₅, i.e., ##STR4##

Radical R as well as radical R₁ may additionally comprise one or morehetero atoms, preferably halogen, (F, Cl, Br) atoms, oxygen atoms orsulphur atoms; they may be located in branches or in the chain, thelatter being preferred. "In the chain" means here a member of a chianconsisting of carbon atoms. Due to their monovalence, halogen atomscannot be located in the chain. Most suitable are O atoms and S atomsonly. Though N-atoms are also possible chain members as --NH-- or--NR'-- groups (R'=an organic radical), they are less desirable, sinceN-compounds, as is well known to those skilled in the art are oftenresponsible for producing undesirable discoloration in course of thepolycondensation process.

Within the chain the S-atoms can be present as sulfide groups, sulfoxidegroups or sulfone-groups, whereas on the chain or on the aromatic ringthey may be present mainly as sulfonate groups.

The following examples may be cited to illustrate radicals R containinghetero atoms: ##STR5## and with O atoms and S atoms in chain position.--(CH₂)₃ --O--(CH₂)₃ -, --(CH₂)₂ --O--(CH₂)₂ --O--(CH₂)₂ --, --(CH₂)₄--O--(CH₂)₄ -, --(CH₂)₄ --S--(CH₂)₄ --, --CH₂)₄ --S--(CH₂)₄ --, ##STR6##

In cases where R is a saturated, open-chained or cyclic alkylene radicala halogen-substitution is satisfactory only, if the compounds either donot or only slightly yield hydrogen halide under the conditions used forpreparation of the polyester. Suitable halogen-substituted alkyleneradicals of this kind are, for example, the radical ##STR7## orperfluorinated alkylene radicals.

Radical R₁ may also contain hetero atoms in similar manner. In thiscase, however, the most suitable substituents are halogen atoms or thesulfonate group, for example,

CH₂ Cl, C₆ H₄ Cl, C₆ H₄ Br, C₆ H₄ SO₃ Na, etc.

The linear polyesters comprising the above, special structural units aschain members are obtained as follows: The usual starting materialswhich are known to be most suitable for preparing high-molecular andparticularly fiber-forming and film-forming linear polyesters arereacted in known manner, while prior to, during or shortly before theend of the polycondensation bifunctional carboxy-phosphinic acids whichmay optionally contain further hetero atoms and/or their esters with alower alcohol of especially from one to four carbon atoms or with diolare added, the latter also forming the diol component of the polyester.It is also possible to use the oligomers of the above carboxy-phosphinicacid-diol esters. It is further possible to use the cyclic anhydrides ofphosphinic-carboxylic acids which form easily and are readilyaccessible. The quantity of the carboxy-phosphinic acid component may befrom about 3-20 mol. % of the total acid component.

The carboxy-phosphinic acids used here have the formula ##STR8## whereinR and R₁ have the aforesaid meaning.

The dicarboxylic acids used as starting materials may be free acids ormay be esterified with lower aliphatic alcohols having preferably fromone to four carbon atoms, especially CH₃ OH, Terephthalic acid ispreferred and may be used with other dicarboxylic acids asco-components. Other suitable acids are, for example, isophthalic acid,5-sulfo-isophthalic acid, 5-sulfopropoxy-isophthalic acid,naphthalene-2,6-dicarboxylic acid, diphenyl-p, p-dicarboxylic acid,p-phenylenediacetic acid, diphenyloxide-p, p'-dicarboxylic acid,diphenoxy-alkane-dicarboxylic acids, transhexahydroterephthalic acid,adipic acid, sebacic acid, 1,2-cyclobutane-dicarboxylic acid etc.

Suitable diol-components are, besides ethylene-glycol, e.g.propane-diol-1,3, butane-diol-1,4 and the higher homologues ofbutane-diol-1,4 as well as, 2,2-dimethyl-propanediol-1,3,1,4-cyclohexane-dimethanol etc., as well as co-componets.

In cases where terephthalic acid is used with additional dicarboxylicacids as disclosed above, it is preferable that the additional acidconstitute not much more than 10 mol. % of the total acid used. Similarconsiderations apply to the composition of the diol component. Forexample, if further diols besides the ethylene-glycol are used ascomponents, their quantity preferably should not substantially exceed 10mol. % of the total diol component.

If the starting materials are free dicarboxylic acids and diols, thefirst step, as usual for these reaction partners, is the esterification,followed by polycondensation. If the starting materials are dicarboxylicacid esters, and especially dimethyl esters, instead of freedicarboxylic acids, the first step is also transesterification which isfollowed by polycondensation, each of these steps using the usualcatalysts.

Of course usual additives (cross-linking agents, delusterants andstabilizers, nucleating agents, coloring agent and fillers etc.) can beadded during the preparation of polyesters, in addition to the usualcatalysts.

Bifunctional carboxyphosphinic acids which are added prior to, during orshortly before termination of the polycondensation and which containstill further hetero atoms, or their esters or their cyclic anhydridescan be prepared as follows:

Carboxyphosphinic acids having but one carbon atom inserted between theP-atom and the COOH-group are obtained, for example, according to thereaction described by H. G. Hennig and G. Hilgetag in J. Prakt. Chem.29, 86 ff (1965), starting from α-Cl or α-Br-acetic acid alkyl estersand phosphonous acid alkyl esters. A carboxymethyl-phenyl-phosphinicacid having e.g. the formula ##STR9## is obtainable by this method.

If R is an alkylene group having two or more carbon atoms, it is usefulto follow the reaction scheme described by V. K. Chajrullin et al aprox.in Z. Obsc. Chim. 37 (1967) No. 3, pg. 710-714, starting fromdichlorophosphines and unsaturated carboxylic acids, such as, forexample: ##STR10## Among the unsaturated acids preference is given tothe use of acrylic acid, methacrylic acid and crotonic acid.

Carboxyphosphinic acids having an aromatic radical (R=arylene) insertedbetween the P and COOH-groups can be prepared for instance according tothe guidelines of the process described by L. D. Quin et al in J. Org.Chem. 27, 4120 (1962) or according to the process disclosed inApplication serial No. (German Patent Application No. P 2346657.1) filedconcurrently herewith.

That latter process consists in reacting halogenobenzoic acid esterswith phosphoneous acid diesters according to the guidelines of anArbusov reaction. The carboxylalkyl-phosphinic acid esters can besaponified e.g. by means of strong inorganic acids or bases.

Carboxyphosphinic acids with R being aralkylene can be prepared byanalogy to Belgian Pat. No. 601,710 from carboxybenzylhalides andphosphoneous acid esters and subsequent saponification of the estergroups to yield free acids.

The carboxyphosphinic acids or their esters or cyclic anhydrides are notvolatile under the conditions of the polyester-formingreaction--contrary to e.g. various diphosphinic acids--so that theformer may be incorporated well and completely by condensation.

The phosphorus-organic structural unit is randomly distributed in themacromolecule of the polyester final product. Occasionally thecarboxyphosphinic acid units may also be present as terminal groups, dueto their random distribution. In order to guarantee the desiredflame-repellent properties, moulding compositions should contain atleast approx. 0,5 wt. % of phosphorus in the polyester, whilst theamount in filaments and fibers should be at least 1 wt. %. Theflame-retarding qualities are further improved, if the P-containingchain members in the polyesters include halides as hetero atoms.

Subsequently, the completely condensed polyesters are spun to filamentsand fibers as usual, stretched and submitted to additional treatment orextruded to yield sheets or, in known manner, worked-up to obtain shapedarticles by press-moulding, injection-moulding or extrusion.Particularly suitable are filaments, fibers, sheets and shaped articlesthe dicarboxylic acid component of which contains mainly terephthalicacid and the diol component of which comprises essentiallyethylene-glycol. All these shaped articles are also an object of thepresent invention.

The fibers and filaments have very good and permanent flame-repellentand self-extinguishing properties. Since they have a good degree ofwhiteness, they have very good dyeing properties for disperse dyestuffsand their receptivity includes acid dyestuffs in colour shades ofaverage to deep intensity. If the P-containing chain membersadditionally include sulfonate groups, the receptivity also extends tobasic dyestuffs. The diglycol portion of the polyesters increases onlyslightly. The tensile strength of the filaments and fibers, second ordertransition temperature, melting point, etc. approximately correspond tothe values of the non-modified polyesters.

Such fibers and filaments are generally useful, for applications wherereadily ignitible textiles and technical articles cannot be tolerated,for example for awning cloths, carpets, curtains etc. It is alsopossible to use these filaments as one of the components inbi-component-filaments in combination with other polymers.

The sheets and shaped articles as well are used whereever serious risksof ignition and fire exist. If the transparency of the shaped articlesis not a matter of concern, their solidity can be enhanced by imbeddingtherein e.g. inorganic fiber materials such as glass fibers, fibers fromquartz, asbestos and carbon in the usual quantities. As examples of suchshaped articles there can be cited casings, structural parts, electricmachinery, mechanical transmission parts in automates, hollow articles,structural units in large-scale computers and sensitive electronicapparatus.

The following examples illustrate the present invention

EXAMPLE 1

1,000 g of dimethylterephthalate are transesterified with 720 ml ofethylene-glycol in the presence of 230 mg of manganacetate 4 H₂ O ascatalyst, the transesterification taking place under nitrogen attemperatures of from 170°-220° C. After completion of the separation ofmethanol 100 g of 2-carboxy-ethyl-methylphosphinic acid (preparationaccording to V. K. Chajrullin et al, Z. obsc. Chim 37 (1967) No. 3, pg.710-714) are added at 220° C. and esterified.

After having added 350 mg of Sb₂ O₃ the reaction mixture is furtherheated and, simultaneously, evacuated slowly so that a pressure of 1torr at 250° C. interior temperature is built up. The polycondensationis carried out at 0.2 torr and at 275° C. until a relative viscosity (1%solution in dichloroacetic acid at 25°) of 1,85 is attained. Meltingpoint 244°-248° C., phosphorus contents: 1.85%.

The condensation product was spun from the melt under the usualconditions and, subsequently, stretched in a proportion of 1:3.65. Thethreads obtained showed a resistance of 33 g/tex at an elongation atbreak of 35%. They were worked up to a tubular knit which was used fordyeing and flame tests.

Dyeing with the acid dyestuffs having the commercial names of

"Supranol Echtrot" (C.I. No. 24,790) (Red)

"Alphanol Echtblau FGLL" (C.I. 62,155) and (Blue)

"Lanaperlgelb 3 G" (C.I. No. 19,025) (Yellow) yielded deep colourshades.

The flammability test was carried out according to the oxygen-indexmethod as per the test regulation ASTM D 2863-70. For that purpose thetubular knit was fitted vertically into the apparatus and flamed fromabove. An artificial oxygen/nitrogen atmosphere was created with aquantity of oxygen which was just enough to allow the test knit to burn.

A value of 29 vol. % of O₂ had been found. A corresponding tubular knitmade of non-modified polyethylene-terephthalate started burning at anoxygen concentration of 20 vol. %.

EXAMPLES 2-8

The test according to example 1 was repeated with differentcarboxyphosphinic acids or their derivatives suitable for incorporationinto polyester molecules. The following table shows the results.

                                      TABLE                                       __________________________________________________________________________                                                  characteristics of              Examples 2-8:                                 polyester  Oxygen-test          Ex.                                                                              Modification   Preparation       quantity                                                                           rel..sup.+  P-  on tubular           No.                                                                              agent          according to:     added                                                                              viscosity                                                                          melting point                                                                        content                                                                           knit                 __________________________________________________________________________        ##STR11##     V. K. Chajrullin et al. Z.obsc. Chim. 38 (1968) Nr. 2,                        S. 288-292        100 g                                                                              1.75 240-242° C.                                                                   1.9%                                                                              30 Vol.%             3                                                                                 ##STR12##     V. K. Chajrullin et al. Z obsc. Chim. 37 (1967) Nr. 3,                        S. 710-714         80 g                                                                              1.89 241-245° C.                                                                   1.6%                                                                              30 Vol. %            4 5                                                                               ##STR13##      U.S. Pat. No. 3,974,243                                                                         90 g 100 g                                                                        1.54 1.37                                                                          243-245° C. 241-243.d                                                  egree. C.                                                                            1.25% 1.4%                                                                        28 Vol.% 29 Vol.                                                              %                    6                                                                                 ##STR14##                       100 g                                                                              1.81 247-249° C.                                                                   1.4%                                                                              29 Vol. %            7                                                                                 ##STR15##     V. K. Chajrullin et al. Z obsc. Chim. 37 (1967) Nr. 2,                        S. 455-460        125 g                                                                              1.79 240-244° C.                                                                   1.7%                                                                              30 Vol. %            8                                                                                 ##STR16##     V. K. Chajrullin et al. Doklady Akad. SSSR 162 (1965)                         Nr. 4, S. 827-828 or Z obsc. Chim. 42 (1972) Nr. 8 S.                         1730-1733          75 g                                                                              1.77 245-247° C.                                                                   1.3%                                                                              27.5 Vol.            __________________________________________________________________________                                                             %                     .sup.+ measured or carried out according to the description of Example 1 

EXAMPLE 9

The experiment as per example 1 was repeated, except that 6 mol. % ofthe DMT was replaced by dimethyl-isophthalate in the transesterificationstep. The polymer melting point was then 236°-238° C. The relativeviscosity was 1.82. Tubular knits made of this material have an oxygenindex value of 30%.

EXAMPLE 10

Example 1 was repeated with the difference that instead of 100 g of2-carboxy-ethyl-methyl-phosphinic acid there are used 75 g of its cyclicanhydride 2-methyl-2,5-dioxo-1-oxa-2-phospholane having formula##STR17## and, instead of 350 mg of Sb₂ O₃ of example 1, the presentexample 10 used 300 mg of GeHPO₃.

The purely white polyester containing 1.5 % of phosphorus was crushed inthe cold. The reduced specific viscosity of the granules was 1.08(measured in phenol/tetrachloroethane=3:2 at 25° C.). The viscosity ofthe granules was increased to 1.36 by condensation of the solid matterin a rotating vessel at 230° C. and at 0.2 torr, condensation period 8hours.

The granules were worked up to plates on an injection moulding machine,the cylinder having temperatures of 260°/270°/260° C., the mouldingtemperature being 20° C. The plates measuring 60×60×2 mm weretransparent and completely colorless, their reduced specific viscositywas 1.25. The impact strength of the plates was examined by means of thedrop hammer test, exposing the plates to the vertical impact of adropping object (drop hammer) from various heights, the plates beingclamped onto a frame. The tip of the drop hammer was shaped as ahemisphere having a radius of 10 mm and a weight of 1 kg. For eachheight 10 plates were submitted to the test. For example, at a givendropping height of 150 cm the impact was strong enough to break 50% ofthe plates. The impact strength of the plates of the example was 200 cm.

Plates being obtained under the same conditions but without thephosphorus modification compound and having a reduced specific viscosityof 1.32, showed an impact strength of 190 cm when submitted to impactunder the same conditions.

For the flammability test the granules were pressed to plates 1.3 mmthick at a temperature between 230° and 250° C. and under a pressure of80 atm. From these plates were cut test specimens measuring 127×12.7 mm.The result of the flammability test according to ASTM D 635-68 was"non-ignitible," the flammability test being carried out according toUnderwriters Laboratories (UL) Subject 94 "SE O."

EXAMPLE 11

Example 10 was repeated with the difference that instead of 75 g of2-methyl-2,5-dioxo-1-oxa-2-phospholane only 35 g of this compound wereused. The phosphorus portion was then 0.7%. The flammability testaccording to ASTM D 635-68 showed the material to be"self-extinguishing.

We claim:
 1. A linear polyester which is the polycondensation product ofa dicarboxylic acid, a diol and a flame-retarding carboxy-phosphinicacid monomer, said monomer being used in an amount of from 3 to 20 molpercent, based on the total amount of dicarboxylic acid and monomer,said monomer being a source of structural units in said polyester of theformula ##STR18## wherein R is saturated, open-chain or cyclic alkylene,arylene or aralkylene having one to 15 carbon atoms, and may contain oneor more hetero atoms selected from F, Cl, Br, O and S, and R₁ is alkylhaving up to six carbon atoms, aryl, or aralkyl and may contain one ormore hetero atoms selected from F, Cl, Br, O and S, provided that in theR and R₁ groups the O, if present, is the oxygen of an ether group, andthe S, if present, is the sulfur of a thioether, sulfoxide, sulfone orsulfonate group.
 2. A linear polyester according to claim 1 whereinR is--CH₂ --CH₂ -- or --C₆ H₄ - and R₁ is CH₃ -- or C₆ H₅ --.
 3. A linearpolyester according to claim 1 wherein the radical R or R₁ contains ahetero atom O or S.
 4. A linear polyester according to claim 1 whereinthe units derived from dicarboxylic acid are essentially terephthalicacid units and the units derived from the diol are essentially units ofa diol of the formulaHO (CH₂)_(n) OHwherein n is 2 to 10, or the diolunits are derived from 1,4-cyclohexane-dimethanol.
 5. A linear polyesteraccording to claim 1 wherein the units derived from dicarboxylic acidare essentially terephthalic acid units and the units derived from diolare essentially ethylene glycol units.
 6. A method of making a linearpolyester which comprises polycondensing a dicarboxylic acid or a loweralkyl ester thereof with a diol in the presence of a flame-retardingphosphorus containing monomer of the general formula ##STR19## or alower alkyl ester or cyclic anhydride of said monomer in an amount ofabout 3 to 20 mole percent of the total acid components wherein thesymbol R of said formula is saturated, open-chain or cyclic alkylenehaving one to 15 carbon atoms, arylene or aralkylene, and R₁ of theformula is alkyl having up to 6 carbon atoms, aryl or aralkyl, andwherein R and R₁ may further contain one or more hetero atoms selectedfrom F, Cl, Br, O and S, provided that in the R and R₁ groups the O, ifpresent, is the oxygen of an ether group, and the S, if present, is thesulfur of a thioether, sulfoxide, sulfone or sulfonate group.
 7. Aprocess according to claim 6 wherein the dicarboxylic acid isterephthalic acid and the diol is ethylene glycol.
 8. Shaped articlesmade by molding or extrusion of the linear polyester of claim
 1. .Iadd.9. A linear polyester which is effectively a polycondensation product ofa dicarboxylic acid, a diol and a flame-retarding amount of acarboxy-phosphinic acid monomer, said monomer being a source ofstructural units in said polyester of the formula ##STR20## wherein R issaturated, open-chain or cyclic alkylene, arylene or aralkylene havingone to 15 carbon atoms, and may contain one or more hetero atomsselected from F, Cl, Br, O and S and R₁ is alkyl having up to six carbonatoms, aryl, or aralkyl and may contain one or more hetero atomsselected from F, Cl, Br, O and S, provided that in the R and R₁ groupsthe O, if present, is the oxygen of an ether group, and the S, ifpresent, is the sulfur of a thioether, sulfoxide, sulfone or sulfonategroup. .Iaddend. .Iadd.
 10. A flame-repellant linear polyester obtainedby incorporating in said polyester by condensation aphosphorus-containing compound having the formula: ##STR21## wherein Ris saturated, open-chain or cyclic alkylene, arylene or aralkylenehaving one to 15 carbon atoms, and may contain one or more hetero atomsselected from F, Cl, Br, O and S, andR₁ is alkyl having up to six carbonatoms, aryl or aralkyl and may contain one or more hetero atoms selectedfrom F, Cl, Br, O and S, provided that in the R and R₁ groups the O, ifpresent, is the oxygen of an ether group, and the S, if present, is thesulfur of a thioether, sulfoxide, sulfone or sulfonate group. .Iaddend..Iadd.
 11. A flame-retarding linear polymer which comprises a modifiedpolyethylene terephthalate having structural units of the formula##STR22## present in an amount sufficient to impart flame-repellantproperties thereof, wherein R is saturated, open-chain or cyclicalkylene, arylene or aralkylene having one to 15 carbon atoms and maycontain one or more hetero atoms selected from F, Cl, Br, O and S, andR₁ is alkyl having up to six carbon atoms, aryl or aralkyl and maycontain one or more hetero atoms selected from F, Cl, Br, O and S,provided that in the R and R₁ groups the O, if present, is the oxygen ofan ether group and the S, if present, is the sulfur of a thioether,sulfoxide, sulfone or sulfonate group. .Iaddend. .Iadd.
 12. Aflame-retarded linear polyester which is effectively a polycondensationproduct of a dicarboxylic acid, a diol and a carboxy-phosphinic acidmonomer present in an amount sufficient to impart flame-retardantproperties to said polyester, said monomer being a source of structuralunits in said polyester of the formula ##STR23## wherein R is saturated,open-chain or cyclic alkylene, arylene or aralkylene having one to 15carbon atoms, and may contain one or more hetero atoms selected from F,Cl, Br, O and S and R₁ is alkyl having up to six carbon atoms, aryl oraralkyl and may contain one or more hetero atoms selected from F, Cl,Br, O and S, provided that in the R and R₁ groups the O, if present, isthe oxygen of an ether group, and the S, if present, is the sulfur of athioether, sulfoxide, sulfone or sulfonate group. .Iaddend. .Iadd. 13.The polyester as defined in claim 12 which comprises a polyethyleneterephthalate. .Iaddend.